Eden Prairie’s water stewards, Part 1: What are impaired waters?

Editor’s note: This 3-part, in-depth feature by Jeff Strate explores how Eden Prairie’s residents, city staff, and watershed leaders are confronting the challenges facing local lakes and streams – from salt runoff to algae blooms. It’s a story of science, stewardship, and community action. This is Part 1.

Retired teacher Judy Berglund has bundled up and trudged 130 yards during snowy winters with an empty bucket along Spyglass Drive to Riverview Road. De-icing salt can trickle off city snowplows at the stop sign. Berglund scoops the spill into the bucket to use sparingly on her own sidewalk. Otherwise, she says, it would wash into the holding pond behind her home.

Chloride, one of the components of salt, can kill aquatic plants and fish. Only a small amount seeps into the Minnesota River from Berglund’s bluff-top neighborhood, but fertilizer runoff from farms, and high bacteria and sediment levels, continue to plague the river. Reaches along Eden Prairie’s southern edge appeared on the 2024 impaired waters list compiled by the Minnesota Pollution Control Agency (MPCA).

Impaired lakes and creeks in Eden Prairie are marked in red in this detail from the 2024 MPCA state map.

Impaired streams and lakes on the 2024 MPCA map resemble dribbles of red marinara sauce. Riley, Rice Marsh, Round, and Staring lakes, the east half of Lake Smetana, stretches of Nine Mile, Purgatory and Riley creeks, and the Minnesota River are marked in shades of red. 

Mitchell, Red Rock, Bryant, Rice, Grass, Duck, Neill, Idlewild, Birch Island and Anderson lakes are not currently listed. But nature’s complexion is ever-changing; some might be added or removed from next year’s list. Eden Prairie is not unusual — Minnesota counts 6,345 impaired waters.

What is impairment?

When lakes and streams fail to meet standards acceptable for human uses like fishing, boating and swimming, the MPCA designates them (or parts of them) impaired. The culprits not only include dissolved chloride but also elevated levels of dissolved nitrogen and phosphorus from lawns and farms, livestock manure, goose and pet poop, grass clippings and tree litter.

Waterborne particles more than 2 microns in size, referred to as “suspended solids,” are also contaminants. Elevated levels of microscopic bits of sand, clay, silt, decaying vegetation, algae and bacteria can harm our waters.

The U.S. Environmental Protection Agency requires each state to adopt water quality standards and to develop plans to fix its impaired waters. The MPCA is charged with overseeing compliance with federal guidelines. Local agencies do the work.

For example, sediments containing phosphorus can be stirred up by bottom-feeding common carp and goldfish. Watershed district carp reduction programs have helped clean up Staring and Purgatory Park lakes and the Riley Creek Chain of Lakes. That chain includes lakes Lucy, Ann and Susan in Chanhassen, as well as Rice Marsh and Riley lakes, which are partially in Eden Prairie. Last year, more than 1,000 carp were removed from Lake Normandale in Bloomington by the Nine Mile Creek Watershed District (NMCWD).

Aluminum sulfate (alum) treatments that clean up lake phosphorus have also been applied over the years at Round, Riley and Bryant lakes. The Riley Purgatory Bluff Creek Watershed District (RPBCWD) approved a contract in August to treat Rice Marsh Lake and re-treat Round Lake with alum.

EP’s legacy

Joni Mitchell’s earworm of a tree-hugger anthem, “Big Yellow Taxi,” doesn’t necessarily tell Eden Prairie’s story. “They paved paradise and put up a parking lot,” Mitchell sang in her 1970 hit — a lament about overdevelopment that doesn’t fit the city’s history.

When “Big Yellow Taxi” was spinning on FM radio in the 1970s, Eden Prairie was still mostly rural and affordable.

Longtime Eden Prairie journalist Mark Weber (an EPLN founder and contributor) wrote that city leaders at the time made investments that ensured a water-friendly and scenic future. The city began purchasing and protecting shorelines and creek corridors from overdevelopment.

Those gifts, however, would require vigilant care as Eden Prairie’s growth began its surge in the 1980s.

Salty and not so salty

As Eden Prairie’s present-day water resources engineer, Patrick Sejkora oversees the total maximum daily load (TMDL) capacity of “anything that’s coming into or out of the pipes.” Sejkora monitors the city’s storm sewer system, street curbing and gutters, and evaluates drainage problems shared with neighboring cities — including chloride from road salt.

City of Eden Prairie Waters Resource Engineer Patrick Sejkora during an August visit to Flagstone Senior Living Community. Photo from Flagstone Facebook platform.

“Once it’s in a lake,” he said, “you really can’t get rid of it.”

That’s why city snowplow drivers are trained to limit the amount of road salt used in variable weather and road conditions. They are certified by the MPCA and are assisted by GPS tracking, street temperature sensors and mobile phone coordination. City crews also apply pre-storm stripes of salt brine mixture on streets to reduce both ice formation and salt use.

(EPLN’s Jim Bayer provided a detailed story on the city’s snowplow drivers on Jan. 19, 2023.)

But chloride levels in Purgatory Creek and six of the seven lakes within its watershed have risen steadily since 2018. Staring Lake’s chloride levels fell slightly in 2023 but remain just shy of concern. 

A commercial parking lot on Valley View Road last winter suggested an over-application of salt.Photo by Jeff Strate

Best management salting protocols seem to be ignored at those institutional, office and commercial parking lots that sport chalky-white asphalt during winter. The MPCA’s Smart Salting training program has a free PDF manual that also applies to private parking lots and snow removal contractors. The Smart Salting program also offers certification, trainings and workshops for individuals and organizations.

The city’s planning department encourages project proposals that require less salt. If a developer’s blueprints show that a structure’s shadows on parking surfaces will be minimized and/or sloped to absorb ice-melting heat from, say, a February sun, planning staff and commissioners will smile.

Purgatory Creek can be engorged by Minnesota River flood waters. The Riverview Road crossing was closed from June 24 and re-opened on July 6, 2024. Photo by Jeff Strate

Rules of the road

Riverview Road in southeast Eden Prairie was closed June 24, 2024, after heavy rains swelled the Minnesota River and its tributaries. Floods that breached around the Rapidan Dam on the Blue Earth River near Mankato and saturated farmland and county ditches from Sleepy Eye to the metro area crept some 900 yards up Purgatory Creek’s corridor. Silt from Blue Earth County soybean fields and ravines helped lather Riverview Road.

Riverview Road is just one of 996 streets, cul-de-sacs and highways* that nestle between Eden Prairie’s scenic lakes, wetlands and creeks. City street crews are busy.

(Note: *Google Maps provides a list of streets in Eden Prairie.)

Blue-green algae is actually a bacteria, cyanobacteria. It can be toxic to humans and pets even though it looks like pea soup. Nine Mile Creek Watershed District photo

Grass clippings, leaves and pet waste contain phosphorus, which washes into storm sewers or directly from lawns into lakes. Blue-green algae binges on phosphorus and can form those toxic blooms. Temporary beach closures this summer were ordered for Riley, Round and Bryant lakes.

Eden Prairie Public Works Director Robert Ellis noted for this report that the city’s annual street-sweeping program typically removes 2,360 cubic yards of debris each year before it clogs or washes into storm sewers. He calculates that to be the cubic size of 2,360 washing machines.

A minimum of three citywide street sweepings are launched each year. The spring sweep begins after the winter melt, collecting loose sand, de-icing material and tree budding debris. The summer sweep gathers loose sand and gravel, grass clippings and tree debris. The fall sweep brushes up twigs and leaves — millions of them. Some streets get four or five sweeps a year because they pass through wooded areas or near construction sites with earth-moving and spillage.

When city contractors repair street cracks, they rout the cracks before sealing them with hot rubber. The router machines blow dust and particles onto streets and sometimes lawns and driveways. 

Jake Sandvig, the city’s street division manager, told EPLN that crews are assigned to blow the debris back onto the street. Sweeping machines and crews then remove the asphalt debris after the sealant hardens — ideally before it rains.

If debris of any kind washes through a sewer grate, two additional traps can keep it from reaching lakes and creeks.

Under street sewer sump.

Eden Prairie’s stormwater system includes 695 sump basins hidden underneath street sewer inflow grates. The city estimates that, on average, these sewer sumps capture 184 cubic yards of sediment and debris each year. Additional sediment is trapped in city and private stormwater detention ponds, which require regular inspections and periodic cleanings.

(Note: The city’s Stormwater and Surface Water webpage provides more details.)

Next in this series

In Part 2, “Eden Prairie’s water stewards” reviews efforts impacting specific waterways in Eden Prairie.
Part 3 provides a review of many of the water stewardship organizations and looks at what individuals can do.

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Editor’s note: Writer Jeff Strate is a founding EPLN board member. EPLN’s Jim Bayer contributed to this series.